These have been called “get out of jail” cards by critics of the scheme, initiated under the Labour Government in the context of Northern Ireland peace negotiations. Angry Loyalists, Conservatives and others believe it amounts to an unconstitutional amnesty, never agreed by the UK Parliament. They are particularly outraged that in the case of John Downey one of the letters, sent to him by the Northern Irish police in error, caused the collapse of the Hyde Park bombing trial. His lawyers had successfully claimed abuse of process before Mr Justice Sweeney in the High Court.

So no wonder Villiers had to talk tough. But is she actually saying anything tough? Actually, no. Her speech in effect signs up to the scheme and suggests the Tories in the Government may huff and puff but will quietly leave it alone. Her statement says nothing new and changes nothing. Her main contention is this:

“They [the letters] will not protect you from arrest or from prosecution and if the police can gather sufficient evidence, you will be subject to all the due processes of law, just like anybody else.”

That’s not new, tough anti-IRA bomber policy – that’s just a description of the status of the letters. They were sent to “on the runs” (OTRs) – potential suspects of often serious terrorist crimes who had moved outside UK jurisdiction. Under the Northern Ireland peace deal those convicted offenders already in prison would be due for early release – they would serve no more than two more years for their offences. But it was difficult to know how such a principle would affect those who had evaded justice – and weren’t likely to want to rush home and put themselves on trial even if two years was the maximum likely sentence.

The charge was later (sensibly) dropped, but now anti-fracking protesters have been successfully prosecuted for another obscure Victorian offence: “besetting” the Cuadrilla test drilling site near Balcombe, West Sussex. Natalie Hynde and Simon Medhurst had superglued themselves to a gate and held up the entry of lorries for two hours.

So what is “besetting” – or “watching and besetting” as the offence is properly termed? And could it become a significant legal weapon in the armoury against protest? The answer to the second question seems to be yes, since the law has also been used against pensioners and other protesters objecting to the cutting down of trees in Sheffield.

The crucial point about the law is that it involves successfully preventing someone going about their legal work – which, of course, in the anti-fracking context (and tree-felling), is exactly what protesters are attempting to do.